[Lab]difference between "diffraction grating" and "linear polarizer" ? I'm recently looking for optical devices to do some experiments at home, like diffraction and polarization, but when I turn to Amazon for the goods, I found that both the sheets I want are marked: 500 lines/mm -- diffraction grating, and linear polarizing sheet(2nd picture of the product shows "500 lines/mm diffraction"). You can click the names to view the corresponding devices on Amazon. Note that this is absolutely not ads, I have to exemplify the dimensions. Maybe that "500 lines/mm" in the polarizing sheet link is not for the polarizer itself, I'm not sure. This "500 lines/mm" confuses me, as the physics text book says, if I wanna observe diffraction, the dimension of the aperture should be comparable to the wave length of visible light(several hundreds of nanometers), thus apertures on the "diffraction grating" should suffice this criterion -- it's 2um/line = 2000 nm/line, and I think this is the interval of apertures, so "500 lines/mm" should be a good choice for diffraction grating. However, the dimension requirement of polarizing sheet was not mentioned in my physics courses, I have no idea how large or small the apertures(or the lines) should be so as to allow polarization, is it also "comparable to the wave length of visible light" ? If there's any flaws in my description, please point out and I'll correct them asap.